Abstract
It has been suggested that oxidation of rod outer segment (ROS) membrane lipids of photoreceptor cells may be involved in light-induced retinal degeneration. All-trans retinal is a potent photosensitizer and its role in mediating photodamage, mainly lipid oxidation by producing singlet oxygen, has been suspected for over two decades as shown in studies using ROS membranes or liposomes. Here we demonstrate that all-trans retinal may actually act as a photosensitizer and produce photooxidation in living cells. Exogenous all-trans retinal caused lipid oxidation under UV light (365nm) in bleached bovine ROS membranes in proportion to either the duration of UV radiation or the concentration of retinal. Similar results were obtained from dark-adapted ROS membranes with retinal released from rhodopsin after irradiation with long wavelength light (530nm). Finally, consistent with previous studies which have implicated that accumulated all-trans retinal may cause light-induced oxidation in photoreceptor cells, intact ellipsoid cells, which are able to quantitatively convert all-trans retinal to all-trans retinol, showed significantly less oxidation compare to those without ellipsoid when exposed to UV light after releasing all-trans retinal with 530nm light. UV did not have much effect when there was no 530nm light treatment. These results indicate that all-trans retinal, which is released from rhodopsin by 530nm light, is photosensitizing component in living cells and causes membrane oxidation in living cells. [J Physiol Sci. 2006;56 Suppl:S177]
